Walker unable to start flatpak apps

I’m using walker on my hyprland installation. I’ve recently installed an app through flatpak (enabled the flatpak service in configuration.nix, installed the apps in the home.nix).
Opening it with flatpak run works fine. They also show up in walker, but when I press enter on them nothing happens.
Walker seems to be running as some service, when I enter walker in the console I don’t see the log output.
Does anyone have a similar problem or know how to fix this? My config is available on github.